1. Technical Field
The subject matter disclosed herein relates to a digital to analog converter. More particularly, the subject matter relates to a tri-level digital to analog converter.
2. Background Art
A digital-to-analog converter (“DAC” or “D-to-A”) is a device that converts a digital (usually binary) code to an analog signal (e.g., a current, voltage, or electric charge). A switched resistor DAC is a type of DAC that contains a parallel network of DAC elements containing resistors. Individual resistors in the network are coupled to either a reference voltage or ground based on the digital input to generate an output analog signal. Accordingly, for a given input digital signal, a first portion of the resistors is connected to the reference voltage and a second portion of the resistors is connected to ground, which wastes power in the form of a path from the reference voltage to ground. This may be most significant for a small input signal case, where around half of the resistors are connected to the reference voltage and the other half of the resistors are connected to ground. Furthermore, an amplifier may be present to amplify the analog signal that was output by the network of DAC elements (e.g., as an audio driver). If an output voltage of the amplifier is centered near ground, there can be a common mode current that flows through the dividing resistors and feedback resistors of the amplifier, increasing a flicker noise in those elements.
Oversampling DACs or interpolating DACs, such as a delta-sigma DAC, use a pulse density conversion technique. Delta-sigma DACs require precision DACs to take a low resolution input word and convert it to a precise analog value. This is typically done with unit DAC elements. However, it is very difficult to match individual elements to the required precision of the overall DAC. In order to overcome this, dynamic element matching (DEM) is typically used, in which an input word is converted into a unit element encoded word, where the individual unit element values are shuffled. Ideally, each element is equally used, thereby averaging out their differences over time.